OD26 - Inverse consistency error as a validation metric for deformable image registration: preliminary implementation research

The aim of this work is to develop a novel automatic voxel-based quantitative measurement approach to evaluate the registration accuracy of a Deformable Image Registration (DIR) algorithm in clinical practice. As the Inverse Consistency Error (ICE) can be computed directly from the deformation vector field (DVF) generated by the Treatment Planning System (TPS), it appears to be a valid surrogate of standard quality assurance metrics to assess the spatial error in the registration process

Electromagnetic turbulent structures: A ubiquitous feature of the edge region of toroidal plasma configurations

Electromagnetic features of turbulent filaments, emerging from a turbulent plasma background, have been studied in four different magnetic configurations: the stellarator TJ-II, the Reversed Field Pinch RFX-mod, a device that can be operated also as a ohmic tokamak, and the Simple Magnetized Torus, TORPEX. By applying an analogous diagnostic concept in all cases, direct measurements of both field-aligned current density and vorticity were performed inside the filament. The inter-machine comparison reveals a clear dependence of the filament vorticity upon the local time-averaged E x B flow shear. Furthermore, a wide range of local beta was explored allowing concluding that this parameter plays a fundamental role in the appearance of filament electromagnetic features

Quantifying multi-Institution KB-plan prediction models transferability in breast cancer radiotherapy: A step forward toward benchmark

Ten Institutes (INST1-INST10) of the MIKAPOCo consortium set their KB plan prediction models of whole breast irradiation (WBI) delivered with tangential fields (TF), by using RapidPlan (Varian Medical System, Inc.) and following the same criteria of contouring and plan model building and validation. DVH prediction bands of organs at risk (heart, ipsilateral lung, contralateral lung and contralateral breast) were exported on 20 new patients from the same Institutes (two patients each). SD of mean predicted DVHs among institutes was assessed as inter-institute variability. The estimated Principal Component (PC1) was con sidered for transferability models evaluation. Transferability cross-validation was further investigated in detail on a larger population for the model showing the poor est transferability (ModelINST6) against one of the models with high transferability (ModelINST3). Results show a limited inter-institute variability of plan prediction models (1.8% for DVH ipsilateral lung) and a satisfactory inter-institute transferability, excepting one institute, confirmed by the extended analyses on a larger cohort of test patients of INST6 (vs. INST3). These achievements pave the way for generating benchmarks for plan prediction in WBI with potentially relevant large-scale applications

Technical Note: An IBEX adaption toward image biomarker standardization

Purpose: Interest in the field of radiomics is rapidly growing because of its potential to characterize tumor phenotype and provide predictive and prognostic information. Nevertheless, the reproducibility and robustness of radiomics studies are hampered by the lack of standardization in feature definition and calculation. In the context of the image biomarker standardization initiative (IBSI), we investigated the grade of compliance of the image biomarker explorer (IBEX), a free open-source radiomic software, and we developed and validated standardized-IBEX (S-IBEX), an adaptation of IBEX to IBSI. Methods: Image biomarker explorer source code was checked against IBSI standard. Both the feature implementation and the overall image preprocessing chain were evaluated. Sections were re-implemented wherever differences emerged: in particular, contour-to-binary-mask conversion, image sub-portion extraction, re-segmentation, gray-level discretization and interpolation were aligned to IBSI. All reported IBSI features were implemented in S-IBEX. On a patient phantom, S-IBEX was validated by benchmarking five different preprocessing configurations proposed by IBSI. Results: Most IBEX feature definitions are IBSI compliant; however, IBEX preprocessing introduces non-negligible nonconformities, resulting in feature values not aligned with the corresponding IBSI benchmarks. On the contrary, S-IBEX features are in agreement with the standard regardless of preprocessing configurations: the percentage of features equal to their benchmark values ranges from 98.1% to 99.5%, with overall maximum percentage error below 1%. Moreover, the impact of noncompliant preprocessing steps has been assessed: in these cases, the percentage of features equal to the standard drops below 35%. Conclusions: The use of standardized software for radiomic feature extraction is essential to ensure the reproducibility of results across different institutions, easing at the same time their external validation. This work presents and validates S-IBEX, a free IBSI-compliant software, developed upon IBEX, for feature extraction that is both easy to use and quantitatively accurate